In refrigeration circuits, some of the oil that lubricates the compressor is entrained in the vapor pumped by the compressor, and the oil circulates throughout the refrigerant circuit. Most refrigerant compressors require the lubricant to reduce friction and help to seal the compression cylinder or cavity. Inevitably, some of the lubricating oil is drawn into the refrigerant vapor stream and circulates throughout the refrigerant circuit and back to the compressor if nothing traps the oil along the way. In conventional refrigerant circuits, the vessel just upstream from the compressor is the “accumulator”, potentially the most likely place for oil to be trapped. But this is typically circumvented by the use of an “oil return hole” near the bottom of the tube that serves as the outlet of the accumulator. While this returns the oil to the compressor, liquid refrigerant can not be stored in the accumulator, as it also would leave by way of the oil return hole. The accumulator is an interesting misnomer in that the typical accumulator can only accumulate liquid briefly, as any liquid refrigerant quickly leaves via an oil return hole.
In circuits using an active charge control (ACC), the oil must be transported through the ACC to the compressor. In a typical ACC, at least one dimension is critical to proper oil return from the ACC to the compressor. If the dimensions within the ACC are not well matched to the size and loading of the compressor, insufficient oil transport from the ACC to the compressor can result.
By way of example, it is desirable to store all inactive liquid refrigerant in the ACC. Refrigerant arriving at the ACC is primarily vapor, but may also include liquid. In either state oil is either entrained in the vapor, or dissolved in the liquid. The vaporized refrigerant passes on through the ACC, but a significant portion of the oil clings to the ACC walls and is trapped there. Liquid arriving at the ACC is trapped there, including the oil dissolved therein.
In circuits using an active charge control (ACC), the oil must be transported through the ACC to the compressor. It has been necessary to provide means of moving oil trapped in the ACC on to the compressor. This was done with a system of splash plates and exit clearances, which caused the oil to become a fine-droplet mist or a tiny bubble consisting of oil surrounding a tiny bit of vapor. The mist and/or bubbles were then entrained in the vapor stream and carried on to the compressor. The problem with this method of oil return is that it is sensitive to the velocity of the refrigerant passing through the ACC, the area of the exit clearance, and even the type of oil used in the system. Careful matching of the compressor and the ACC was required.
As above addressed, and as is well known in the art, typical ACC dimensions are critical to proper oil return from the ACC to the compressor. If the dimensions within the ACC are not well matched to the size and loading of the compressor, insufficient oil transport from the ACC to the compressor can result.